Chemical treatment steel sheet, and method for producing chemical treatment steel sheet

ABSTRACT

A chemical treatment steel sheet includes a steel sheet; a Fe—Sn alloy layer which is formed on at least one surface of the steel sheet; an Sn layer which is formed on the Fe—Sn alloy layer; and a chemical treatment layer that is formed on the Sn layer, and contains a 0.01 to 0.1 mg/m 2  of Zr compounds in terms of an amount of metal Zr and 0.01 to 5 mg/m 2  of phosphate compounds in terms of an amount of P. The total Sn content of the Fe—Sn alloy layer and the Sn layer is 0.1 to 15 g/m 2  of Sn in terms of the amount of metal Sn.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a chemical treatment steel sheet, and amethod for producing a chemical treatment steel sheet.

Priority is claimed on Japanese Patent Application No. 2014-207921,filed on Oct. 9, 2014, the content of which is incorporated herein byreference.

RELATED ART

When continuously using a metal, there is a concern that corrosion mayoccur. In the related art, various technologies are suggested so as toprevent corrosion from occurring in a metal. Examples of thetechnologies which are suggested include a technology of performingplating with respect to a metal sheet, and a technology of performingvarious surface treatments with respect to a surface of a metal sheet orplating.

Here, a Ni-plated steel sheet, a Sn-plated steel sheet, a Sn-based alloyplated steel sheet, and the like are used to manufacture a metalcontainer that is intended to preserve drinks or food.

In a case of using a Ni-plated steel sheet, a Sn-plated steel sheet, ora Sn-based alloy plated steel sheet as a steel sheet for metalcontainers (hereinafter, referred to as “steel sheet for containers”)that is intended to preserve drinks or food, a chemical treatment isperformed with respect to a surface of the plated steel sheet withhexavalent chromium so as to secure adhesion between the steel sheet anda coating or a film, and corrosion resistance in many cases. Thechemical treatment using a hexavalent chromium-containing solution isreferred to as a chromate treatment.

However, the hexavalent chromium that is used in the chromate treatmentis harmful in an environmental aspect, and thus a chemical treatmentfilm such as Zr-phosphorous film has been developed as a substitute forthe chromate treatment that is performed for the steel sheet forcontainers in the related art. For example, Patent Document 1 disclosesa steel sheet for containers which includes a chemical treatment filmthat contains Zr, phosphoric acid, a phenol resin, and the like.

PRIOR ART DOCUMENT Patent Document

[Patent Document 1] Japanese Unexamined Patent Application, FirstPublication No. 2007-284789

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In a case of using the chemical treatment steel sheet, in which thechemical treatment film disclosed in Patent Document 1 is formed on asurface of a Sn-plated steel sheet, as a steel sheet for containersintended to store acidic contents such as acidic fruit, it is possibleto use the chemical treatment steel sheet in a state in which thechemical treatment film and the contents come into direct contact witheach other without carrying out coating on the surface of the chemicaltreatment film. Since coating is not performed on the surface of thechemical treatment film, Sn that is eluted from the Sn-coated steelsheet and O₂ in the contents cause a reaction, and thus it is possibleto prevent oxidation of the contents.

However, from a result of examination by the present inventors, thepresent inventors have obtained the following finding. Since thechemical treatment film, in which a surface is not subjected to coating,is discolored and turns yellow (yellowing) in accordance with avariation with the elapse of time, there is a problem in that theexterior appearance deteriorates.

In addition, in a case of using the chemical treatment steel sheet, inwhich the chemical treatment film disclosed in Patent Document 1 isformed on a surface of a Sn-plated steel sheet, as the steel sheet forcontainers, the chemical treatment steel sheet is required to haveadditional corrosion resistance.

The invention has been made in consideration of the above-describedcircumstances, and an object thereof is to provide a chemical treatmentsteel sheet having excellent yellowing resistance and corrosionresistance, and a method for producing the chemical treatment steelsheet.

Means for Solving the Problem

The invention employs the following means to solve the above-mentionedproblems and to accomplish the object.

(1) According to an aspect of the invention, a chemical treatment steelsheet includes: a steel sheet; a Fe—Sn alloy layer which is formed on atleast one surface of the steel sheet; an Sn layer which is formed on theFe—Sn alloy layer; and a chemical treatment layer that is formed on theSn layer, and contains a 0.01 to 0.1 mg/m² of Zr compounds in terms ofthe amount of metal Zr and 0.01 to 5 mg/m² of phosphate compounds interms of an amount of P. The total Sn content of the Fe—Sn alloy layerand the Sn layer is 0.1 to 15 g/m² of Sn in terms of the amount of metalSn.

(2) In the chemical treatment steel sheet according to (1), the chemicaltreatment layer may contain 0.08 mg/m² or less of Zr compounds in termsof the amount of metal Zr.

(3) In the chemical treatment steel sheet according to (2), the chemicaltreatment layer may contain 0.06 mg/m² or less of the Zr compounds interms of the amount of metal Zr.

(4) In the chemical treatment steel sheet according to any one of (1) to(3), the chemical treatment layer may contain 0.02 mg/m² or more of theZr compounds in terms of the amount of metal Zr.

(5) In the chemical treatment steel sheet according to any one of (1) to(4), the chemical treatment layer may contain 4 mg/m² or less of thephosphate compounds in terms of the amount of P.

(6) In the chemical treatment steel sheet according to any one of (1) to(5), the chemical treatment layer may contain less than 1 mg/m² of thephosphate compounds in terms of the amount of P.

(7) In the chemical treatment steel sheet according to any one of (1) to(6), the chemical treatment layer may contain 0.03 mg/m² or more of thephosphate compounds in terms of the amount of P.

(8) In the chemical treatment steel sheet according to any one of (1) to(7), when a variation amount in a yellowness index before and afterstorage for 4 weeks in an environment of a temperature of 40° C. and ahumidity of 80% at one measurement point on an outermost surface of thechemical treatment layer is set as ΔYI, an average value of the ΔYIobtained at the measurement points included in a unit area of theoutermost surface may be less than 1.7.

(9) In the chemical treatment steel sheet according to any one of (1) to(8), the total Sn content of the Fe—Sn alloy layer and the Sn layer maybe 0.5 to 13 g/m² of Sn in terms of the amount of metal Sn.

(10) In the chemical treatment steel sheet according to any one of (1)to (9), a surface of the chemical treatment layer may not be coated witha film or a coating.

(11) According to another aspect of the invention, a method forproducing a chemical treatment steel sheet includes: a plating processof forming an Sn coated layer that contains 0.1 to 15 g/m² of Sn interms of an amount of metal Sn on a surface of a steel sheet; a reflowprocess of forming an Fe—Sn alloy layer and an Sn layer by performingreflow treatment to the Sn coated layer; and a chemical treatmentprocess of forming a chemical treatment layer on the Sn layer byperforming an electrolytic treatment in a chemical treatment liquid,which contains 10 ppm to less than 500 ppm of Zr ions, 10 to 20000 ppmof F ions, 10 to 3000 ppm of phosphate ions, and 100 to 30000 ppm in atotal amount of nitrate ions and sulfate ions and of which a temperatureis set to equal to or higher than 5° C. and lower than 90° C., underconditions of a current density of 0.5 to 20 A/dm² and an electrolytictreatment time of 0.05 to 10 seconds, or by performing an immersiontreatment in the chemical treatment liquid for an immersion time of 0.2to 100 seconds.

(12) In the method for producing a chemical treatment steel sheetaccording to (11), the chemical treatment liquid may contain 100 ppm toless than 500 ppm of Zr ions, 100 to 17000 ppm of F ions, 20 to 2000 ppmof phosphate ions, and 1000 to 20000 ppm in the total amount of nitrateions and sulfate ions.

Effects of the Invention

According to the aspects, it is possible to provide a chemical treatmentsteel sheet having excellent yellowing resistance and corrosionresistance, and a method for producing the chemical treatment steelsheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a view schematically showing an example of a chemicaltreatment steel sheet in which a Fe—Sn alloy layer, an Sn layer and achemical treatment layer are formed on a single surface of a steelsheet.

FIG. 1B is a view schematically showing an example of the chemicaltreatment steel sheet in which the Fe—Sn alloy layer, the Sn layer andthe chemical treatment layer are formed on both surfaces of the steelsheet.

FIG. 2 is a flow chart showing an example of a flow of a method ofproducing the chemical treatment steel sheet.

FIG. 3 is a graph showing a result of Example 1.

EMBODIMENTS OF THE INVENTION

Hereinafter, a preferred embodiment of the invention will be describedin detail with reference to the accompanying drawings. Furthermore, inthis embodiment, the same reference numeral will be given to constituentelements having the same configuration, and a redundant descriptionthereof will be omitted.

<With Respect to Configuration of Chemical Treatment Steel Sheet>

First, a configuration of a chemical treatment steel sheet according toan embodiment of the invention will be described in detail withreference to FIG. 1A and FIG. 1B. FIG. 1A and FIG. 1B schematically showa layer structure of the chemical treatment steel sheet according tothis embodiment when seen from a lateral side.

As shown in FIG. 1A and FIG. 1B, a chemical treatment steel sheet 10according to this embodiment includes a steel sheet 103, a Fe—Sn alloylayer 105 a, an Sn layer 105 b, and a chemical treatment layer 107.Furthermore, the Fe—Sn alloy layer 105 a, the Sn layer 105 b and thechemical treatment layer 107 may be formed on a single surface of thesteel sheet 103 as shown in FIG. 1A, or may be formed on both surfacesof the steel sheet 103 as shown in FIG. 1B.

[With Respect to Steel Sheet 103]

The steel sheet 103 is used as a base metal of the chemical treatmentsteel sheet 10 according to this embodiment. With respect to the steelsheet 103 that is used in this embodiment, a known steel sheet 103 thatis used as a steel sheet for containers may be used without particularlimitation. In addition, with respect to a method for producing thesteel sheet 103 and a material thereof, a steel sheet 103, which isproduced through from a typical billet producing process to a knownprocess such as hot-rolling, pickling, cold-rolling, annealing, andtemper rolling, may be used without particular limitation.

It is preferable that the sheet thickness of the steel sheet 103 is 0.05to 1 mm in consideration of practicability and economic efficiency in acase of being used as a steel sheet for containers.

[With Respect to Fe—Sn Alloy Layer 105 a and Sn Layer 105 b]

The Fe—Sn alloy layer 105 a is formed on a surface of the steel sheet103 and the Sn layer 105 b is formed on the Fe—Sn alloy layer 105 a. TheFe—Sn alloy layer 105 a and the Sn layer 105 b are barrier-type platinglayers. The barrier-type plating layer is a plating layer that reducescorrosion of the steel sheet 103 by forming a metal film of Sn on thesurface of the steel sheet 103 by using Sn that is a moreelectrochemically noble metal in comparison to Fe that constitutes thesteel sheet 103 that is the base metal in order for a corrosion factornot to act on the base metal.

Hereinafter, an example of the Fe—Sn alloy layer 105 a and the Sn layer105 b according to this embodiment will be described in detail withreference to FIGS. 1A and 1B.

As shown in FIGS. 1A and 1B, the Fe—Sn alloy layer 105 a is formed on atleast a single surface of the steel sheet 103, and the Sn layer 105 b isformed on the Fe—Sn alloy layer 105 a. Although details will bedescribed later, the Fe—Sn alloy layer 105 a and the Sn layer 105 b areformed by performing a tin melting treatment (reflow treatment) andthereby alloying a part of an Sn coated layer (not shown) with Fe of thesteel sheet 103 in a state that the Sn coated layer (not shown) isformed on the surface of the steel sheet 103.

The Sn coated layer (not shown) in this embodiment may be configuredonly by Sn, or may contains an impurity or a slight amount of element inaddition to Sn.

The Sn coated layer (not shown) is formed to secure the corrosionresistance and weldability of the chemical treatment steel sheet 10. Snitself has high corrosion resistance, and an Sn alloy formed through thetin melting treatment also has excellent corrosion resistance andweldability.

After forming the Sn coated layer (not shown), the tin melting treatmentis performed. According to this, the Fe—Sn alloy layer 105 a is formedon the steel sheet 103, and the Sn layer 105 b is formed on the Fe—Snalloy layer 105 a.

The total Sn content of the Fe—Sn alloy layer 105 a and the Sn layer 105b is 0.1 to 15 g/m² of Sn per single surface in terms of the amount ofmetal Sn.

Sn has excellent workability, weldability, and corrosion resistance.When the tin melting treatment is performed after Sn plating, it ispossible to further improve the corrosion resistance of the chemicaltreatment steel sheet 10, and it is possible to attain a more preferredsurface exterior appearance (mirror surface exterior appearance) of thechemical treatment steel sheet 10. The Fe—Sn alloy layer 105 a and theSn layer 105 b are required to contain 0.1 g/m² or more of Sn per singlesurface in terms of the amount of metal Sn so as to exhibit theabove-described effect.

However, when the total Sn content of the Fe—Sn alloy layer 105 a andthe Sn layer 105 b is greater than 15 g/m² per single surface in termsof the amount of metal Sn, the above-described effect with Sn becomessaturated. In addition, when the total Sn content of the Fe—Sn alloylayer 105 a and the Sn layer 105 b is greater than 15 g/m² per singlesurface in terms of the amount of metal Sn, this is not preferable froman economical aspect. For the above-described reason, the total Sncontent of the Fe—Sn alloy layer 105 a and the Sn layer 105 b is set to15 g/m² or less per single surface in terms of the amount of metal Sn.

More preferably, the total Sn content of the Fe—Sn alloy layer 105 a andthe Sn layer 105 b is 0.5 g/m² to 13 g/m² per single surface in terms ofthe amount of metal Sn. When the total Sn content of the Fe—Sn alloylayer 105 a and the Sn layer 105 b is 0.5 g/m² to 13 g/m² per singlesurface in terms of the amount of metal Sn, it is possible to increasethe corrosion resistance of the chemical treatment steel sheet 10preferably by Sn and further reduce the production cost.

In addition, the thick ratio between the Fe—Sn alloy layer 105 a and theSn layer 105 b is not particularly limited. The Fe—Sn alloy layer 105 aand the Sn layer 105 b are only required to contain the above-describedamount of Sn in total.

The Fe—Sn alloy layer 105 a contain 0.001 to 100 g/m² of Fe per singlesurface in terms of the amount of metal Fe. In addition, the Fe—Sn alloylayer 105 a may contain unavoidable impurities other than Sn and Fewhich are mixed-in in a production process and the like.

In the Fe—Sn alloy layer 105 a, the total of the amount of Fe containedin terms of the amount of metal Fe and the amount of Sn in terms of theamount of metal Sn is 50% by mass or more. Preferably, in the Fe—Snalloy layer 105 a, the total amount of Fe contained in terms of theamount of metal Fe and the amount of Sn contained in terms of the amountof metal Sn is 70% by mass or more.

The Sn layer 105 b may be constitute of Sn only or may contain 0.001 to6 g/m² in terms of the amount of metal Fe in addition to Sn. Inaddition, the Sn layer 105 b may contain unavoidable impurities whichare mixed-in in a production process and the like.

In the Sn layer 105 b, the amount of Sn in terms of the amount of metalSn is 50% by mass or more. Preferably, in the Sn layer 105 b, the amountof Sn in terms of the amount of metal Sn is 70% by mass or more.

In a case of using the steel sheet 103, on which the Fe—Sn alloy layer105 a and the Sn layer 105 b are formed, as a steel sheet for containerswhich store acidic contents such as acidic fruits, a coating treatmentis not performed on a surface that comes into contact with the acidiccontents. When the Sn layer 105 b and the acidic contents come intodirect contact with each other, Sn in the Sn layer 105 b is eluted, andis likely to react with O₂ contained in the contents. According to this,oxidation of the acidic contents is prevented.

However, SnO, which is generated through a reaction between Sn and O₂,is a yellow compound. According to this, the surface of the steel sheet103, on which the Fe—Sn alloy layer 105 a and the Sn layer 105 b areformed, is discolored and turns yellow (yellowing) according to theformation of SnO. When the yellowing occurs, the contents may bemisunderstood as decaying, and thus the yellowing is not preferable.According to this, the present inventors have thought of a configurationin which the chemical treatment layer 107 is formed on the Sn layer 105b so as to suppress the yellowing of the surface of the steel sheet 103on which the Fe—Sn alloy layer 105 a and the Sn layer 105 b are formed.

The present inventors have obtained the following finding. In a casewhere the chemical treatment layer 107 that contains Zr is formed on theSn layer 105 b, the adhered amount of the chemical treatment layer 107becomes equal to or greater than a predetermined amount, the chemicaltreatment layer 107 is gradually discolored and turns yellow.

Accordingly, the present inventors have made an additionalinvestigation, and have found a chemical treatment steel sheet 10 inwhich the yellowing of the chemical treatment layer 107 that contains Zris suppressed, and satisfactory external appearance is maintained. Thatis, in the invention, the chemical treatment layer 107, of which anadhered amount is in a specific range and which contains Zr, is formedon the Sn layer 105 b.

[With Respect to Chemical Treatment Layer 107]

As shown in FIG. 1A and FIG. 1B, the chemical treatment layer 107 isformed on the Sn layer 105 b. The chemical treatment layer 107 is acomposite film layer that mainly contains a Zr compound, and contains a0.01 to 0.1 mg/m² of Zr compounds per single surface in terms of theamount of metal Zr and 0.01 to 5 mg/m² of phosphate compounds per singlesurface in terms of the amount of P.

In a case where two films of a Zr film that contains the Zr compoundsand a phosphate film that contains the phosphate compounds are formed onthe Sn layer 105 b in a state in which the two films overlap each other,a certain degree of effect is obtained on corrosion resistance oradhesion, but the effect is not sufficient in practical use. However, asis the case with this embodiment, when the Zr compounds and thephosphate compounds exist in the chemical treatment layer 107 in a stateof being partially mixed, it is possible to attain more excellentcorrosion resistance and adhesion in comparison to the case where thetwo films are formed to overlap each other as described above.

The Zr compound, which is contained in the chemical treatment layer 107according to this embodiment, has a function of improving corrosionresistance, adhesion, and working adhesion. Examples of the Zr compoundsaccording to this embodiment include Zr oxide, Zr phosphate, Zrhydroxide, Zr fluoride, and the like, and the chemical treatment layer107 contains a plurality of the Zr compounds. A preferred combination ofthe Zr compounds is a combination of the Zr oxide, the Zr phosphate, andthe Zr fluoride.

In a case where the amount of the Zr compounds contained in the chemicaltreatment layer 107 is 0.01 mg/m² or more per single surface in terms ofthe amount of metal Zr, corrosion resistance, adhesion of a coating andthe like, and yellowing resistance, which are suitable in practical use,are secured.

On the other hand, as the amount of the Zr compounds containedincreases, corrosion resistance, adhesion, and adhesion of a coating andthe like are improved. However, when the amount of the Zr compoundscontained is greater than 0.1 mg/m² per single surface in terms of theamount of metal Zr, yellowing characteristics of the chemical treatmentlayer 107 in accordance with a variation with the passage of time becomesignificant. Accordingly, the chemical treatment layer 107 according tothis embodiment contains 0.01 mg/m² to 0.1 mg/m² of Zr compounds persingle surface in terms the amount of metal Zr.

The upper limit of the amount of Zr compounds contained is preferably0.08 mg/m² or less per single surface in terms of the amount of metalZr, and more preferably 0.06 mg/m² or less per single surface in termsof the amount of metal Zr.

In addition, the lower limit of the amount of the Zr compounds containedis preferably 0.02 mg/m² or more per single surface in terms of theamount of metal Zr.

When the amount of the Zr compounds contained is set to theabove-described range, it is possible to attain more excellent corrosionresistance, adhesion, adhesion of a coating and the like, and yellowingresistance.

The chemical treatment layer 107 further contains one or more kinds ofphosphate compounds in addition to the above-described Zr compound.

The phosphate compounds according to this embodiment has a function ofimproving corrosion resistance, adhesion, and working adhesion. Examplesof the phosphate compounds according to this embodiment include Fephosphate, Sn phosphate, Zr phosphate, and the like which are formedthrough a reaction between phosphate ions and compounds which areincluded in the steel sheet 103, the Fe—Sn alloy layer 105 a, the Snlayer 105 b, and the chemical treatment layer 107. The chemicaltreatment layer 107 may contain one kind or two or more kinds of thephosphate compounds.

The greater the amount of the phosphate compounds contained in thechemical treatment layer 107 is, the further corrosion resistance,adhesion, and working adhesion of the chemical treatment steel sheet 10are improved. Specifically, in a case where the amount of the phosphatecompounds contained in the chemical treatment layer 107 is greater than0.01 mg/m² per single surface in terms of the amount of P, corrosionresistance, adhesion, adhesion of working and the like, and yellowingresistance, which are suitable in practical use, are secured.

On the other hand, as the amount of the phosphate compounds containedincreases, corrosion resistance, adhesion, and working adhesion are alsoimproved. However, when the amount of the phosphate compounds containedis greater than 5 mg/m² per single surface in terms of the amount of P,the yellowing characteristics of the chemical treatment layer 107 inaccordance with a variation with the passage of time become significant.Accordingly, the chemical treatment layer 107 according to thisembodiment contains 0.01 mg/m² to 5 mg/m² of phosphate compounds persingle surface in terms the amount of P.

The upper limit of the amount of phosphate compounds contained ispreferably 4 mg/m² or less per single surface in terms of the amount ofP, and more preferably less than 1 mg/m² per single surface in terms ofthe amount of P.

In addition, the lower limit of the amount of the phosphate compoundscontained is preferably 0.03 mg/m² or more per single surface in termsof the amount of P. When the amount of the phosphate compounds containedis set to the above-described range, it is possible to attain moreexcellent corrosion resistance, adhesion, working adhesion, andyellowing resistance.

Furthermore, the chemical treatment layer 107 may further containunavoidable impurities which are mixed-in in a production process andthe like in addition to the Zr compounds and the phosphate compound. Inaddition, in a case where the chemical treatment layer 107 contains Cr,the upper limit of the amount of Cr contained is 2 mg/m².

The chemical treatment steel sheet 10 according to this embodimentincludes the above-described chemical treatment layer 107, and thusexhibits excellent yellowing resistance. For example, when the chemicaltreatment steel sheet 10 is used for storage for 4 weeks in anenvironment of a temperature of 40° C. and a humidity of 80%, a value(hereinafter, referred to as “ΔYI value”), which is obtained byextracting a YI value of the chemical treatment steel sheet beforestorage from a YI value (yellowness index) of the chemical treatmentsteel sheet after storage, is 1.7 or less. That is, the ΔYI value in acase of storage for 4 weeks in an environment of a temperature of 40° C.and a humidity of 80% is 1.7 or less.

The YI value is a value obtained by digitizing tristimulus values(perceiving sensitivity of red, blue, and yellow which are sensed byeyes of human beings) of a color. As the YI value shows a value that ishigher on a positive side, yellow becomes dark. As the YI value shows avalue that is higher on a negative side, bluish white becomes dark.Accordingly, after storage in the above-described environment, in a casewhere the ΔYI value is a positive value, this case represents anincrease in the yellowness index, and in a case where the ΔYI value is anegative value, this case represents a decrease in the yellowness indexand an increase in the degree of bluish-whiteness.

Furthermore, the YI value is calculated by substituting tristimulusvalues X, Y, and Z obtained by using a white measurement meter into thefollowing Expression (1).

YI value=100(1.28X−1.06Z)÷Y  (1)

Here, in a case where the ΔYI value is greater than 1.7, it is possibleto perceive that an object turns yellow. On the other hand, in a casethe chemical treatment steel sheet 10 according to this embodiment isstored for 4 weeks in an environment of a temperature of 40° C. and ahumidity of 80%, the ΔYI value before and after storage is 1.7 or less.That is, in a case of comparing the yellowness index of the chemicaltreatment steel sheet 10 after storage for 4 weeks in an environment ofa temperature of 40° C. and a humidity of 80%, and the yellowness indexof the chemical treatment steel sheet 10 before storage, it is difficultto perceive an increase (yellowing) in the yellowness index of thechemical treatment steel sheet 10. According to this, in the chemicaltreatment steel sheet 10 according to this embodiment, the yellownessindex in the exterior appearance does not vary with the passage of time,and satisfactory exterior appearance can be maintained for a long periodof time.

Furthermore, in this embodiment, the performance of maintaining thesatisfactory exterior appearance for a long period of time is referredto as “yellowing resistance”.

As described above, the chemical treatment steel sheet 10 according tothe present embodiment has excellent yellowing resistance and corrosionresistance. Accordingly, it is possible to use the chemical treatmentsteel sheet 10 as a steel sheet for container when the surface of thechemical treatment layer 107 is not coated with film or lacquer.

<With Respect to Layer Structure of Chemical Treatment Steel Sheet 10>

As described above, the chemical treatment steel sheet 10 includes theFe—Sn alloy layer 105 a on the steel sheet 103, the Sn layer 105 b onthe Fe—Sn alloy layer 105 a and the chemical treatment layer 107 on theSn layer 105 b. That is, in the chemical treatment steel sheet 10, thesteel sheet 103 and the Fe—Sn alloy layer 105 a are in contact with eachother, and another layer is not provided between the steel sheet 103 andthe Fe—Sn alloy layer 105 a. Similarly, in the chemical treatment steelsheet 10, the Fe—Sn alloy layer 105 a and the Sn layer 105 b are incontact with each other, and another layer is not provided between theFe—Sn alloy layer 105 a and the Sn layer 105 b. Furthermore, in thechemical treatment steel sheet 10, the Sn layer 105 b and the chemicaltreatment layer 107 are in contact with each other, and another layer isnot provided between the Sn layer 105 b and the chemical treatment layer107.

<With Respect to Method of Measuring Amount of Component Contained>

Here, for example, the amount of metal Sn in the Fe—Sn alloy layer 105 aand the Sn layer 105 b can be measured by using a fluorescent X-raymethod. In this case, the calibration curve with respect to the amountof metal Sn is created in advance by using a known sample formeasurement of the amount of metal Sn, and the amount of metal Sn isrelatively specified by using the calibration curve that is created.

For example, the amount of metal Zr and the amount of P in the chemicaltreatment layer 107 can be measured by quantitative analysis such asfluorescent X-ray analysis. In addition, it is possible to specifyexistence of a compound in the chemical treatment layer 107 byperforming analysis with X-ray photoelectron spectroscopy (XPS).

Furthermore, the method of measuring each component is not limited tothe above-described method, and a known measurement method can beapplied thereto.

<With Respect to Method of Measuring YI Value>

Measurement of the YI value (yellowness index) may be performed by usinga spectrophotometer based on JIS Z-8722 condition c. With regard to ameasurement type, the measurement can be performed through SCI(including regular reflection light) measurement that is lesssusceptible to an effect by a surface property. In addition, with regardto measurement conditions, it is important to perform the measurementunder constant conditions such as a constant light source, constanthumidity, and a constant temperature.

Furthermore, in measurement of the YI value, for example, it ispreferable to measure YI values at a plurality of measurement pointssuch as arbitrary 20 points per 1 m², and to use an average valuethereof. Here, the measurement points represent a plurality of arbitrarymeasurement points on a single surface at the outermost surface portionof the chemical treatment layer 107. In addition, it is preferable thatthe measurement points are set to points which are spaced away from eachother by at least 10 cm. Specifically, in a case of a large sheet havingdimensions of 1 mx 1 m, it is preferable measurement points are sampled,and points spaced away from each other by 10 cm or more are sampled toperform measurement.

<With Respect to Method of Producing Chemical Treatment Steel Sheet>

Next, a method of producing the chemical treatment steel sheet 10according to this embodiment will be described in detail with referenceto FIG. 2. FIG. 2 is a flowchart showing an example of a flow of themethod of producing the chemical treatment steel sheet according to thisembodiment.

[Pre-Treatment Process]

In the method of producing the chemical treatment steel sheet 10according to this embodiment, first, a known preliminary treatment isperformed with respect to the steel sheet 103 as necessary (step S101).

[Plating Process]

Then, the Sn coated layer (not shown) is formed on a surface of thesteel sheet 103 (step S103). The method of forming the Sn coated layer(not shown) is not particularly limited. A known electric platingmethod, a method of immersing the steel sheet 103 in molten Sn forplating, and the like can be used.

[Tin Melting Treatment (Reflow Treatment) Process]

After forming the Sn coated layer (not shown), a tin melting treatment(reflow treatment) is performed (step S104). According to the tinmelting treatment, the Fe—Sn alloy layer 105 a and the Sn layer 105 bare formed on the steel sheet 103.

The tin melting treatment is performed by heating the steel sheet 103which has the Sn coated layer (not shown) at 200° C. or higher after theSn coated layer (not shown) is formed and thereby causing the Sn layer(not shown) to be melted once. After the heating, rapid cooling isperformed. According to the tin melting treatment, Sn in the Sn coatedlayer (not shown) which is positioned at the steel sheet side 103 isalloyed with Fe in the steel sheet 103, and thereby the Fe—Sn alloylayer 105 a is formed and the remainder Sn forms the Sn layer 105 b.

[Chemical Treatment Process]

Then, the chemical treatment layer 107 is formed on the Sn layer 105 bthrough a cathode electrolytic treatment or an immersion treatment (stepS105).

The chemical treatment layer 107 is formed through a cathodeelectrolytic treatment or an immersion treatment, but a chemicaltreatment liquid is used in any case. The chemical treatment liquidaccording to this embodiment contains 10 ppm to less than 500 ppm of Zrions, 10 ppm to 20000 ppm of F ions, 10 ppm to 3000 ppm of phosphateions, and 100 ppm to 30000 ppm in a total amount of nitrate ions andsulfate ions.

In addition, the nitrate ions and the sulfate ions may be contained inthe chemical treatment liquid in a total amount of 100 ppm to 30000 ppm.Both of the nitrate ions and the sulfate ions may be contained in thechemical treatment liquid, or only any one of the nitrate ions and thesulfate ions may be contained in the chemical treatment liquid.

It is preferable that the chemical treatment liquid contains 100 ppm toless than 500 ppm of Zr ions, 100 ppm to 17000 ppm of F ions, 20 ppm to2000 ppm of phosphate ions, and 1000 ppm to 20000 ppm in a total amountof nitrate ions and sulfate ions.

When the concentration of the Zr ions is set to 100 ppm or greater, itis possible to more reliably prevent a decrease in an adhered amount ofZr. In addition, when the concentration of the F ions is set to 100 ppmor greater, it is possible to more reliably prevent white turbidity ofthe chemical treatment layer 107 in accordance with precipitation of aphosphate.

Similarly, when the concentration of the phosphate ions is set to 20 ppmor greater, it is possible to more reliably prevent white turbidity ofthe chemical treatment layer 107 in accordance with precipitation of thephosphate.

When the total concentration of the nitrate ions and the sulfate ions isset to 1000 ppm or greater, it is possible to more reliably prevent adecrease in adhesion efficiency of the chemical treatment layer 107.

In a case where the total concentration of the nitrate ions and thesulfate ions is less than 1000 ppm, the adhesion efficiency of the Zrions is low, and thus the amount of Zr contained in the chemicaltreatment layer 107 decreases. Accordingly, this case is not preferable.On the other hand, when the total concentration of the nitrate ions andthe sulfate ions is greater than 20000 ppm, the adhesion efficiency ofthe Zr ions is high, and thus the amount of Zr contained in the chemicaltreatment layer 107 excessively increases. Accordingly, this case is notpreferable.

Furthermore, when the upper limits of the respective components in thechemical treatment liquid are set to the above-described values, it ispossible to more reliably reduce the production cost of the chemicaltreatment layer 107.

It is preferable that pH of the chemical treatment liquid is in a rangeof 3.1 to 3.7, and more preferably approximately 3.5. Nitric acid,ammonia, and the like may be added to the chemical treatment liquid foradjustment of pH thereof as necessary. Furthermore, even in any of thechemical treatment liquid that is used in the electrolytic treatment andthe chemical treatment liquid that is used in the immersion treatment,it is preferable to satisfy the conditions of pH of the chemicaltreatment liquid.

It is preferable that a temperature of the chemical treatment liquid isequal to or higher than 5° C. and lower than 90° C. In a case where thetemperature of the chemical treatment liquid is lower than 5° C.,formation efficiency of the chemical treatment layer 107 is poor, and isnot economically efficient. Accordingly, this case is not preferable.Furthermore, in a case where the temperature of the chemical treatmentliquid is 90° C. or higher, a structure of the chemical treatment layer107 that is formed is not uniform, and a defect such as cracking and amicro-crack occurs. The defect becomes the origin of corrosion and thelike, and thus this case is not preferable. In addition, even in any ofthe chemical treatment liquid that is used in the electrolytic treatmentand the chemical treatment liquid that is used in the immersiontreatment, it is preferable to satisfy the temperature conditions of thechemical treatment liquid.

Furthermore, when the temperature of the chemical treatment liquid isset to be higher than a surface temperature of the steel sheet 103 onwhich the Fe—Sn alloy layer 105 a and the Sn layer 105 b are formed,reactivity of the chemical treatment liquid increases at an interface,and thus adhesion efficiency of the chemical treatment layer 107 isimproved. According to this, it is preferable that the temperature ofthe chemical treatment liquid is higher than the surface temperature ofthe steel sheet 103 on which the Fe—Sn alloy layer 105 a and the Snlayer 105 b are formed.

[Case of Forming Chemical Treatment Layer 107 by Electrolytic Treatment]

It is preferable that a current density in the electrolytic treatment is0.5 A/dm² to 20 A/dm². In a case where the current density is less than0.5 A/dm², the adhered amount of the chemical treatment layer 107decreases, and an electrolytic treatment time may be longer, and thusthis case is not preferable. In addition, in a case where the currentdensity is greater than 20 A/dm², the adhered amount of the chemicaltreatment layer 107 becomes excessive, and in the chemical treatmentlayer 107 that is formed, a portion that is not sufficiently adhered maybe washed out (peeled off) in a washing process through water washingafter the electrolytic treatment. Accordingly, this case is notpreferable.

It is preferable that the electrolytic treatment time is 0.05 seconds to10 seconds. In a case where the electrolytic treatment time is shorterthan 0.05 seconds, the adhered amount of the chemical treatment layer107 decreases, and desired performance is not obtained. Accordingly,this case is not preferable. On the other hand, in a case where theelectrolytic treatment time is longer than 10 seconds, the adheredamount of the chemical treatment layer 107 becomes excessive, and in thechemical treatment layer 107 that is formed, a portion that is notsufficiently adhered may be washed out (peeled off) in a washing processthrough water washing after the electrolytic treatment. Accordingly,this case is not preferable.

[Case of Forming Chemical Treatment Layer 107 by Immersion Treatment]

The chemical treatment layer 107 according to this embodiment may beformed through an immersion treatment using the chemical treatmentliquid. In a case of forming the chemical treatment layer 107 throughthe immersion treatment, the steel sheet 103 including the Fe—Sn alloylayer 105 a and the Sn layer 105 b is immersed in the above-describedchemical treatment liquid for 0.2 to 100 seconds.

In a case where an immersion time is shorter than 0.2 seconds, theadhered amount of the chemical treatment layer 107 is not sufficient,and thus this case is not preferable. On the other hand, in a case wherethe immersion time is longer than 100 seconds, the adhered amount of thechemical treatment layer 107 becomes excessive, and in the chemicaltreatment layer 107, a portion that is not sufficiently adhered may bewashed out (peeled off) in a washing process through water washing afterthe electrolytic treatment. Accordingly, this case is not preferable.

Furthermore, in formation of the chemical treatment layer according tothis embodiment, tannic acid may be further added to the chemicaltreatment liquid. When the tannic acid is added to the chemicaltreatment liquid, the tannic acid reacts with Fe in the steel sheet 103,and a film of tannic acid Fe is formed on the surface of the steel sheet103. The film of the tannic acid Fe improves rust resistance andadhesion, and is preferable.

As a solvent of the chemical treatment liquid, for example, deionizedwater, distilled water, and the like can be used. Electric conductivityof the solvent of the chemical treatment liquid is preferably 100/cm orless, more preferably 5 μS/cm or less, and still more preferably 3 μS/cmor less. However, the solvent of the chemical treatment liquid is notlimited thereto, and can be appropriately selected in accordance with amaterial to be dissolved, a formation method, formation conditions ofthe chemical treatment layer 107, and the like. However, it ispreferable to use deionized water or distilled water from aspects ofindustrial productivity based on stability in an adhered amount of eachcomponent, cost, and environment.

As a supply source of Zr, for example, a Zr complex such as H₂ZrF₆ canbe used. Zr in the Zr complex exists as Zr⁴⁺ in the chemical treatmentliquid through a hydrolysis reaction in accordance with an increase inpH at a cathode electrode interface. The Zr ions perform dehydration andcondensation reaction with a hydroxyl group (—OH) that exists on a metalsurface in the chemical treatment liquid to form a compound such as ZrO₂and Zr₃(PO₄)₄.

[Post-Treatment Process]

Then, a known post-treatment is performed as necessary with respect tothe steel sheet 103 on which the Fe—Sn alloy layer 105 a, the Sn layer105 b and the chemical treatment layer 107 are formed (step S107).

Through the treatment performed in this flow, the chemical treatmentsteel sheet 10 according to this embodiment is produced.

EXAMPLES

Hereinafter, the chemical treatment steel sheet and the method ofproducing the chemical treatment steel sheet according to thisembodiment of the invention will be described in detail with referenceto Examples. In addition, the following Examples are examples of thechemical treatment steel sheet and the method of producing the chemicaltreatment steel sheet according to the embodiment of the invention, andthe chemical treatment steel sheet and the method of producing thechemical treatment steel sheet according to the embodiment of theinvention are not limited to the following examples.

Example 1

Hereinafter, first, verification was made as to how the YI value variesbefore and after storage for 4 weeks in an environment of a temperatureof 40° C. and a humidity of 80% while varying the amount of Zr containedin the chemical treatment layer. Furthermore, the amount of Zr containedand the YI value were measured by the above-described method.

In Example 1, a steel sheet, which is typically used as a steel sheetfor containers, was used as a base metal, and the Fe—Sn alloy layer andthe Sn layer were formed on the steel sheet. The total amount of Sncontained in the Fe—Sn alloy layer and the Sn layer was 2.8 g/m² persingle surface in terms of the amount of metal Sn. Furthermore, aplurality of samples including chemical treatment layers, in which theamounts of Zr compounds contained were different from each other, wereproduced by changing the concentration of Zr ions in the chemicaltreatment liquid. Here, the amount of phosphate compounds contained ineach sample was set to 3.0 mg/m² per single surface in terms of theamount of P.

Obtained Results are shown in FIG. 3.

In FIG. 3, the horizontal axis represents the amount of Zr compounds(the amount of metal Zr) contained in the chemical treatment layer, andthe vertical axis represents a value (ΔYI value) obtained by subtractinga YI value before storage from a YI value after storage. As is clearfrom FIG. 3, in a case where the amount of Zr contained was 0.01 to 0.10mg/m² per single surface in terms of the amount of metal Zr, the ΔYIvalue was 1.7 or less, and an increase in the yellowness index inaccordance with storage with the passage of time was not recognized.

From the results, when the amount of Zr compounds contained in thechemical treatment layer was set to the predetermined range, it could beseen that the produced chemical treatment steel sheet 10 had excellentyellowing resistance.

From the results, when the amount of Zr compounds contained in thechemical treatment layer was set to the predetermined range, it could beseen that the produced chemical treatment steel sheet 10 had excellentyellowing resistance.

Example 2

Next, a steel sheet, which is typically used as a steel sheet forcontainers, was used as a base metal, the Fe—Sn alloy layer and the Snlayer are formed on the steel sheet. The total amount of Sn contained inthe Fe—Sn alloy layer and the Sn layer is shown in Table 1.Subsequently, the chemical treatment layer was formed on the Sn layer.The amount of metal Zr and the amount of P in the chemical treatmentlayer is shown in Table 1.

With respect to respective samples which were produced as describedabove, the ΔYI value before and after storage for 4 weeks in anenvironment of a temperature of 40° C. and a humidity of 80% wasmeasured. The ΔYI value were measured by the above-described method.

<Evaluation of Corrosion Resistance>

As a corrosion resistance test liquid, 3% acetic acid was used. Thechemical treatment steel sheet as the sample was cut out to a dimensionof φ 35 mm. The cut-out sample was placed on an inlet of a heatresistant bottle into which the corrosion resistance test liquid wasput, and was fixed thereto. After performing a heat treatment at 121° C.for 60 minutes, a contact portion between the sample and the corrosionresistance test liquid was observed to evaluate the degree of corrosionof the sample. Specifically, the following ten-step evaluation wasperformed by using an area of a portion that is not corroded withrespect to the total area of the contact portion between the sample andthe corrosion resistance test liquid. Furthermore, a score is 5 pointsor greater, the steel sheet can be used as a steel sheet for container.

10 points: 100% to 90%

9 points: less than 90% and equal to or greater than 80%

8 points: less than 80% and equal to or greater than 70%

7 points: less than 70% and equal to or greater than 60%

6 points: less than 60% and equal to or greater than 50%

5 points: less than 50% and equal to or greater than 40%

4 points: less than 40% and equal to or greater than 30%

3 points: less than 30% and equal to or greater than 20%

2 points: less than 20% and equal to or greater than 10%

1 point: less than 10% and equal to or greater than 0%

In a corrosion resistance evaluation item, 10 points to 9 points aredescribed as “Very Good”, 8 points to 5 points are described as “Good”,and 4 points or less are described as “Not Good”.

TABLE 1 Chemical treatment steel sheet Coated layer Chemical treatmentlayer Amount of Amount of Amount of Characteristic evaluation Sym- metalSn metal Zr P Corrosion ΔYI bol (g/m²) (mg/m²) (mg/m²) resistance valueExamples A1  0.12 0.06 2.0 Good 1.0 A2 14.2 0.08 2.1 Very Good 1.3 A3 2.6 0.014 2.4 Very Good 0.6 A4 10.3 0.09 1.8 Very Good 1.3 A5  4.40.013 0.017 Very Good 0.3 A6  6.7 0.02 4.7 Very Good 0.8 A7  9.7 0.0452.7 Very Good 1.0 A8  9.9 0.04 3.8 Very Good 1.1 A9  6.6 0.05 0.9 VeryGood 0.7 A10  5.9 0.07 0.025 Very Good 0.7 A11  1.0 0.03 0.9 Very Good0.3 A12  1.2 0.01 0.2 Very Good 0.2 Com- a1  0.04 0.20 3.6 Not Good 3.1parative a2 12.9 0.004 0.012 Very Good 5.2 Examples a3 21.0 0.02 0.003Very Good 5.5

As shown in Table 1, in Examples A1 to A12, the corrosion resistance andthe yellowing resistance were excellent. On the other hand, inComparative Examples a1 to a3, any one or both of the corrosionresistance and the yellowing resistance was poor.

Example 3

A steel sheet, which is typically used as a steel sheet for containers,was used as a base metal, and a chemical treatment was performed on aFe—Sn alloy layer and a Sn layer having the amount of metal Sn as shownin the following Table 2 under conditions shown in the following Table 3to form a chemical treatment layer. With respect to each sample, thecorrosion resistance and the yellowing resistance were measured by thesame method as described above.

Results are shown in Table 4.

TABLE 2 Coated layer Amount of Sym- metal Sn bol (g/m²) Examples B1 5.7B2 10 B3 2.1 B4 8.1 B5 10 B6 6.4 B7 1.1 B8 1.1 B9 13 B10 10 B11 13 B1212 B13 12 B14 14 B15 3.2 B16 8.9 B17 15 B18 6.3 B19 11 B20 12 B21 10 B2212 B23 1.5 B24 5.0 B25 10 B26 13 B27 0.8 B28 15 B29 1.6 B30 10Comparative b1 5.3 Examples b2 14 b3 15 b4 6.6 b5 4.4 b6 12 b7 1.6 b8 14b9 1.6

TABLE 3 Chemical treatment Immer- Chemical treatment bath sion Phos-Bath Electrolytic treat- phate Nitrate Sulfate temp- treatment ment Sym-Zr ion F ion ion ion ion erature Current Time Time bol (ppm) (ppm) (ppm)(ppm) (ppm) (° C.) (A/dm²) (sec) (sec) Exam- B1  11  4502  2417  7511 2347 40 12  9.6 ples B2 498  6845  2970 11436  271 26 15  7.7 — B3 246  10  2654  3330 15635 26  7.4  1.4 — B4  45 19834  1045  8438  6822 6719  9.4 — B5 148  5049   11  2114  9613 82 10  1.0 — B6 493 18930 29384 4769  7819 88  4.5  0.6 — B7 198  5893  447  104 — 50 13  8.6 — B8  2616494  260 29183 — 55 14  3.9 — B9 225 11088  1361 —  109 36  7.8  5.2 —B10  67 11623  2424 — 29384 11 11  9.8 — B11  53  4790  799  1994  4575 6 13  4.2 — B12 292  2284  977 10142  2391 89  4.2  0.5 — B13 373  4914 428  2612  8253 58  0.6  4.7 — B14  12  1150  1752  5522  5581 32 19 5.2 — B15 362  9569  2159  7347 11536 28 12.2  0.06 — B16 188 12891 2393  9696  2550 70  5.4  9.8 — B17 365 11670  430 11017  557 78 — —  0.23 B18  71  8528  2528  1383  3375 71 — —  98.2 B19 108 15216  2963 707  908 27 19.6  4.1 — B20 382  4923  2834  3847  2532 35 15.3  5.3 —B21 391  104  2802  961 16123 43 16.1  5.2 — B22 299 16723  1674 11373 8290 63 18.7  7.5 — B23  47  8855   20 17999  1263 58  6.7  3.6 — B24437 18400  1909 23041  4648 48 10.9  2.1 — B25  70  7503  2109  683   3990 10.3  5.6 — B26 142  2649  2713 19284   28 65 10.2  4.4 — B27 475 1546   66   78  983 81  4.7  2.6 — B28  65 15006  1639   48 19612 29 3.6  7.6 — B29 418  7502  277  5606 15419 40  9.1  5.9 — B30  93 12474 1581 16262  7721 55  4.8  8.7 — Com- b1 890 26340  326  2546 12929 76 1.1  8.3 — parative b2  4   3  1201  9249 10129 59  3.1  9.0 — Exam- b3322  6537   2 33532 32039 43  3.7  0.2 — ples b4 393  7286  3325   43  18 97  2.2  9.8 — b5 152  8345  2076 14856  8024  2 34  7.0 — b6 13013783   48  5887  8899 72  0.3 13.7 — b7 435  3744   275  2117  2848 8418.8  0.02 — b8 187 13886  1770   240  2950 23 — —  0.08 b9  4  5602  177  3606  5418 35 — — 135

TABLE 4 Chemical treatment layer Amount of Amount Characteristicevaluation Sym- metal Zr of P Corrosion ΔYI bol (mg/m²) (mg/m²)resistance value Examples B1 0.04 4.5 Very Good 1.3 B2 0.04 1.7 VeryGood 0.8 B3 0.05 0.9 Very Good 0.7 B4 0.07 1.8 Very Good 1.1 B5 0.02 0.9Very Good 0.4 B6 0.03 0.6 Very Good 0.4 B7 0.04 3.8 Very Good 1.2 B80.02 2.8 Very Good 0.7 B9 0.01 0.8 Very Good 0.3 B10 0.04 2.8 Very Good1.0 B11 0.02 0.6 Very Good 0.3 B12 0.02 3.3 Very Good 0.9 B13 0.02 1.9Very Good 0.6 B14 0.04 3.3 Very Good 1.1 B15 0.02 3.0 Very Good 0.8 B160.02 3.2 Very Good 0.8 B17 0.03 0.4 Very Good 0.4 B18 0.08 2.9 Very Good1.4 B19 0.03 1.0 Very Good 0.5 B20 0.03 1.2 Very Good 0.5 B21 0.03 3.6Very Good 1.0 B22 0.04 3.4 Very Good 1.1 B23 0.02 0.8 Very Good 0.4 B240.02 2.0 Very Good 0.6 B25 0.04 0.7 Very Good 0.5 B26 0.02 3.6 Very Good0.9 B27 0.04 1.5 Very Good 0.7 B28 0.02 2.0 Very Good 0.6 B29 0.06 1.8Very Good 1.0 B30 0.02 3.3 Very Good 0.8 Comparative b1 0.007 2.7 VeryGood 5.0 Examples b2 0.007 2.7 Very Good 6.5 b3 0.02 0.002 Very Good 5.1b4 0.006 4.5 Very Good 5.7 b5 0.008 1.2 Very Good 4.8 b6 0.005 0.2 VeryGood 5.4 b7 0.003 2.2 Very Good 5.2 b8 0.004 1.7 Very Good 7.2 b9 0.0021.7 Very Good 7.2

As shown in Table 4, in Examples B1 to B30, the corrosion resistance andthe yellowing resistance were excellent. On the other hand, inComparative Examples b1 to b9, the corrosion resistance was excellent,but the yellowing resistance was poor.

Hereinbefore, preferred embodiment of the invention has been describedin detail with reference to the accompanying drawings, but the inventionis not limited to the example. It should be understood by those skilledin the art that various modification examples and variations may be madein a scope of the technical sprit described in claims, and these alsopertain to the technical scope of the invention.

INDUSTRIAL APPLICABILITY

According to the embodiment, it is possible to provide a chemicaltreatment steel sheet having excellent yellowing resistance andcorrosion resistance, and a method for producing the chemical treatmentsteel sheet.

BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS

-   -   10: CHEMICAL TREATMENT STEEL SHEET    -   103: STEEL SHEET    -   105 a: Fe—Sn ALLOY LAYER    -   105 b: Sn layer    -   107: CHEMICAL TREATMENT LAYER

1. A chemical treatment steel sheet comprising: a steel sheet; a Fe—Snalloy layer which is formed on at least one surface of the steel sheet;an Sn layer which is formed on the Fe—Sn alloy layer; and a chemicaltreatment layer that is formed on the Sn layer, and contains 0.01 to 0.1mg/m² of Zr compounds in terms of an amount of metal Zr and 0.01 to 5mg/m² of phosphate compounds in terms of an amount of P, wherein a totalSn content of the Fe—Sn alloy layer and the Sn layer is 0.1 to 15 g/m²of Sn in terms of an amount of metal Sn.
 2. The chemical treatment steelsheet according to claim 1, wherein the chemical treatment layercontains 0.08 mg/m² or less of the Zr compounds in terms of the amountof metal Zr.
 3. The chemical treatment steel sheet according to claim 2,wherein the chemical treatment layer contains 0.06 mg/m² or less of theZr compounds in terms of the amount of metal Zr.
 4. The chemicaltreatment steel sheet according to claim 1, wherein the chemicaltreatment layer contains 0.02 mg/m² or greater of the Zr compounds interms of the amount of metal Zr.
 5. The chemical treatment steel sheetaccording to claim 1, wherein the chemical treatment layer contains 4mg/m² or less of the phosphate compounds in terms of the amount of P. 6.The chemical treatment steel sheet according to claim 1, wherein thechemical treatment layer contains less than 1 mg/m² of the phosphatecompounds in terms of the amount of P.
 7. The chemical treatment steelsheet according to claim 1, wherein the chemical treatment layercontains 0.03 mg/m² or greater of the phosphate compounds in terms ofthe amount of P.
 8. The chemical treatment steel sheet according toclaim 1, wherein when a variation amount in a yellowness index beforeand after storage for 4 weeks in an environment of a temperature of 40°C. and a humidity of 80% at one measurement point on an outermostsurface of the chemical treatment layer is defined as ΔYI, an averagevalue of the ΔYI obtained at the measurement points included in a unitarea of the outermost surface is less than 1.7.
 9. The chemicaltreatment steel sheet according to claim 1, wherein the total Sn contentof the Fe—Sn alloy layer and the Sn layer is 0.5 to 13 g/m² of Sn interms of an amount of metal Sn.
 10. The chemical treatment steel sheetaccording to claim 1, wherein a surface of the chemical treatment layeris not coated with a film or a coating.
 11. A method for producing achemical treatment steel sheet, comprising: a plating process of formingan Sn coated layer that contains 0.1 to 15 g/m² of Sn in terms of theamount of metal Sn on a surface of a steel sheet; a reflow process offorming an Fe—Sn alloy layer and an Sn layer by performing a reflowtreatment to the Sn coated layer; and a chemical treatment process offorming a chemical treatment layer on the Sn layer by performing anelectrolytic treatment in a chemical treatment liquid, which containsequal to or greater than 10 ppm and less than 500 ppm of Zr ions, 10 to20000 ppm of F ions, 10 to 3000 ppm of phosphate ions, and 100 to 30000ppm in a total amount of nitrate ions and sulfate ions and of which atemperature is set to equal to or higher than 5° C. and lower than 90°C., under conditions of a current density of 0.5 to 20 A/dm² and anelectrolytic treatment time of 0.05 to 10 seconds, or by performing animmersion treatment in the chemical treatment liquid for an immersiontime of 0.2 to 100 seconds.
 12. The method for producing a chemicaltreatment steel sheet according to claim 11, wherein the chemicaltreatment liquid contains 100 ppm to less than 500 ppm of Zr ions, 100to 17000 ppm of F ions, 20 to 2000 ppm of phosphate ions, and 1000 to20000 ppm in a total amount of nitrate ions and sulfate ions.